The field of producing universal or DC electric motors has been developing for many years. At the outset, soft soldering or brazing of coiled wires to commutators was employed, but the need for high quality motors which were reliable and economically attractive has resulted in the growth and increased utilization of commutator fusing to prepare such motors. Furthermore, at the same time, the development of tang-type commutators as compared to the prior slotted type to increase the ease with which the armature lead wires could be attached to the commutator bars was also developed for such purposes. An apparatus for the efficient and rapid commutator fusing of both the tang and slotted types of commutators is shown in U.S. Pat. No. 3,045,103. That apparatus has permitted the increased production of such motors on a large scale, with relatively uniform quality. Indeed, this apparatus has been used for many years on a large scale for such commutator fusing. However, with the current need for extremely fine quality control and uniform commutator fusing in such motors, when produced on a mass scale, the search has continued for means to adapt such apparatus for such purposes.
The need for such careful quality control arises from the very nature of commutator fusing itself. Thus, as compared to spot welding processes, in commutator fusing techniques, the electrodes generally employed to heat the armature wires and commutator bars are high resistance electrodes, and the parts to be fused are heated by the heat dissipated by these electrodes. Since the lead wires are normally insulated, sufficient current must be applied to the electrodes so that they can be heated to a temperature sufficient to remove the lead wire insulation, and this must be carried out for a short enough period of time so as not to damage the wires themselves. It can therefore be seen that the amount of heat brought to bear upon the joint must be controlled to a very significant degree. Similar results occur in commutator brazing, employing high temperature solder alloys.
In the past, various apparatus have been employed for thermal monitoring in a number of fields. In particular, various photo-sensitive means have been utilized to accomplish such monitoring. For example, U.S. Pat. No. 3,435,173 to Connoy et al utilizes in one embodiment thereof, induction heating through an induction heating coil to weld the ends of saw bands together. This patent employs a photo-sensitive cell to respond to light rays emanating from the weld zone as to the weld temperature rises, and subsequently to terminate current flow at the proper instant. This apparatus, however, cannot achieve anywhere near the degree of control, particularly over inaccessible locations, nor the high quality uniform product which can be achieved in accordance with the present invention.
U.S. Pat. No. 3,781,504 to Harnden, Jr. employs a bolometer to control induction cooking appliances. In particular, the patentee utilizes a hollow radiant energy propogation conduit for the transmission of temperature sensing data.
In addition, U.S. Pat. No. 2,438,160 to Green discloses an alternative apparatus for the control of swaging temperatures employing a caesium suboxide photocell to detect infrared light emitted from a rod or wire emerging from a heating furnace on its way to a swarfing machine, and U.S. Pat. No. 2,640,137 to Ketchledge discloses temperature control means in brazing operations, such as with regard to the end seals of submarine cables. The patentee in the latter case employs a photocell comparison technique, i.e., by comparing the radiations from the work and those from the lamp filament to obtain equal temperatures.
In each of these cases, however, the patentees have been employing various temperature sensitive devices to measure the intensity of the glow or emission from a metallic object upon its heating. These devices therefore generally operate upon a principal similar to that of a thermopile, that is where the radiation is measured by the electromotive force by a temperature rise between two metals. The search has therefore continued for means to not only more accurately measure the temperature of a given material, and to not be bound by the radiation of visible light therefrom, but furthermore for means to utilize this result to control fusing and brazing apparatus for the achievement of a high degree of accuracy therewith.
Finally, in "Practical Applications of Infrared Techniques" by Riccardo Vanzetti, John Wiley and Sons, 1972, the author discloses the monitoring of the metal temperature in spot welding systems by the use of optical fibers. The author then employs a photodetector, such as a silicon or PBS cell to display the measured results on an oscilloscope. Furthermore, in Chapter 4 of this book, the author discusses a number of different thermal measuring devices, similar to those shown in the "ABC's of Infrared" by Burton Bernard, Howard W. Sams and Co., 1970.
The search has, however, continued for a number of years to develop an economically feasible and efficient method for actually controlling the current commercial machinery being utilized for commutator fusing or brazing.